This invention relates to a method of production of a wire shaped composite addition material, i.e., a linear additive, which is effective to perform deoxidation, desulfurization, control of the shape of inclusions and other treatments when added to iron and steel in a molten state, e.g. pig iron, steel, cast iron and cast steel.
It is known that various materials such as calcium, magnesium, aluminium and rare earths have the effect of deoxidation and desulfurization on moten iron and steel when added thereto. They are therefore used in suitable combinations. However, they have the disadvantage of being low in yield when added to the molten metal by a simple plunging method. This is particularly true in the case of calcium and magnesium wherein because of the low boiling points of these materials the yield is only several percents. Moreover, they raise the problem of air pollution by the gas and smoke they generate as they burn when they are added to the molten metal. Added disadvantages are that these addition agents are not only readily oxidized but also highly reactive with moisture in the air, so that difficulty is experienced in storing them. In order to overcome these shortcomings it has heretofore been proposed to protect such reactive addition materials by enclosing them tightly with a covering of iron or steel so that a composite material is obtained. Such composite addition materials have been proposed in the form of rods and wires.
If a covering is applied to the addition material, the problem of moisture absorption and oxidation will be greatly reduced or eliminated. Also, since the covering is made of iron or steel, it has no deleterious effects on the molten steel, to which the addition of the composite material is made. During the process of addition, the covering protects the reactive addition material, and as the covering material has a comparatively high melting point, it will delay the release of the addition material into the molten metal. This enables the addition material to penetrate deep into the molten metal prior to its release and reaction with the melt. Therefore losses of addition material and smoke development due to reactions at the melt surface are avoided and a very efficient use of the adding material can be obtained.
If the composite material is in the form of wire it can be handled with ease and the amount of the addition material added to the molten metal can readily be controlled. This is of special advantage if the composite material is to be added to the molten metal in the mold of continuous casting or to a stream of molten metal during pouring. However advantages can also be found for the addition of such wire shaped composite materials to the molten metal in other locations such as ladles or furnaces.
Methods for the production of linear additives as described above have been proposed, all of which have certain disadvantages:
In one method of production of such linear additives known in the art, a pipe of iron or steel is filled with an addition material and a composite wire of a desired cross-sectional area comprising the addition material can be produced by reducing the cross-sectional area. This method has a disadvantage in that the composite wire produced is short in length, as it is difficult to produce a composite wire of large length by this method.
Calcium, magnesium and aluminum are available in powder or particulate form. If they are in this form, the weight ratio of each agent to the other agents can readily be controlled by suitable mixing of the powders or particulates. Proposals have been made to use a method wherein a mixture of one or more addition agents in powder or particulate form are contained as a core in a tape of iron or steel which is formed into a tube shape as it moves along the path of its movement so that it may serve as a covering. Some disadvantages are associated with this method. When this method is used, the addition agent or agents forming the core are low in coherence and the core is not compact. Therefore, the core has a high air content. Difficulty is experienced in sealing the joint of the tape formed into a tube shape, so that the composite wire produced lacks the ability to keep the core out of contact with air. As a result, the core is readily oxidized or gets damp while the linear additive is stored. The joint of the covering sometimes fails, resulting in the core separating itself from the covering.